1. Field of the Invention:
This invention concerns a ball-and-socket joint system such as is used in jointed devices, particularly in multiarticulate arms.
2. Description of the Prior Art:
Multiarticulate arms are, for example, used in the construction of robots. If they include a great enough number of "phalanges", such arms enable simulation of mechanisms having distributed elasticity and/or deformation. Connected to other mechanisms, they thus enable construction of devices which are often called "probes" and which, when they are affixed at one of their ends, e.g., to a robot, and hold at their other end a tool such as a spot welder, drill, paint gun, etc., enable positioning the tool around an obstacle by turning it. With the help of such probes, large spaces within which work must be done may be entered through a relatively small-sized opening. Such a probe was described in French Pat. No. 77-02387 filed Jan. 28, 1977 for a "Multiarticulate arm for robot or automation." In the abovementioned patent, as in other patents in the same field, different types of ball-and-sockets are used. Some can be dislocated at any moment and, to prevent this, the elements making up the joint must be preloaded using springs. Such preloading increases internal friction and stress, thereby reducing the life of the ball-and-sockets while increasing the power necessary to operate them. For other types of ball-and-sockets, dislocation is prevented by crimping. This operation is very advantageous both from the point of view of wear and of required power, but it makes the device impossible or difficult to disassemble. Furthermore, reassembly usually requires changing the parts making up the ball-and-socket joints.
Also known are ball-and-sockets which cannot be disassembled when they are in normal operating position but which can be easily disassembled when the component parts are placed in a special position not reached during normal use. These ball-and-sockets have several important drawbacks which practically preclude their use in multiarticulate arms. These drawbacks flow essentially from the fact that such ball-and-socket joints are composed essentially of two parts. The first part is composed of a convex spherical element limited by two parallel planes disposed symmetrically on either side of the sphere's center. Such spherical element may be connected to a rod by means of a hole perpendicular to the two planes and passing through its center. The second element is composed of a concave bearing surface of the same radius as the preceding element, formed in a generally cylindrical piece the axis of which passes through the axis of the sphere.
To enable assembly of the two elements, the element with the concave sphere is equipped with a notch which allows the spherical element to move up to the point at which the centers of the two spheres are identical. This requires that the axis of revolution of the convex spherical element and that of the concave spherical element be perpendicular. The two elements can then be pivoted with relation to each other so as to bring the two axes into alignment. The two elements can then be moved with relation to each other in oscillating motions of limited height and rotational motions around their respective axes.
The fact that these ball-and-socket joints are composed of only two elements means that although the concave spherical element can be connected to a tubular "phalanx" of large diameter, the convex spherical element can be connected to a phalanx only by a central shaft of small diameter. In addition, this must be disassembled to allow assembly of the two elements of the ball-and-socket joint. Unfortunately, the construction of synchronized phalanx probes, such as those for which the instant invention is preferentially intended, requires that a system for inter-phalanx synchronization be passed through the center of said joints.
The small-diameter shaft required by the jointing system described above makes passage of such a synchronization system through its center practically impossible. It should be noted finally that the possibility of having ball-and-socket joint elements capable of performing rotations at any angles about their respective axes of revolution is of no use for the construction of multiarticulate arms having only two degrees of freedom enabling them to assume any curvature in any plane containing the axis common to all the phalanges when these are aligned.